This invention relates to a sheet stripping device, and in particular, to apparatus for supporting a sheet stripping finger at a predetermined position and for moving the stripping device into and out of engagement with a moving sheet support surface from which a sheet of material is to be removed.
In many automatic copying machines, and in particular, in the automatic xerographic copying process, it is important to unerringly and repeatedly remove copy sheets from the photoreceptor surface (photosensitive plate) during the course of the copying process. When the sheet removal or stripping device fails, the copy sheet carried on the photoreceptor surface is generally carried forward into subsequent processing stations where the sheet can produce a malfunctioning of the stations involved or, in the extreme case, cause damage to the machine.
Due to the fact that the photoreceptor surface in a xerographic machine may be easily damaged by mechanical contact therewith, various non-contact stripping devices have been proposed. One of the more common type devices is the vacuum stripper wherein the sheet of material to be removed is pulled off from the photoreceptor surface by vacuum. This requires a fairly large vacuum and precise location and design of the vacuum stripping ports to assure positive stripping in all instances. Further, under abnormal conditions, the sheet may still adhere to the photoreceptor surface and be carried therewith into subsequent processing stations causing damage to the machine and destruction of the sheet. "Puffer" stripping systems have also been utilized. These systems, which rely on a blast of air against the lead edge of the sheet material to be removed, usually require a large volume of high pressure air. These air blasts are generally discharged a significant distance away from the copy. This leads to air turbulances in the machine, which, in the case of unfused copy, leads to toner disturbances on the copy sheet with resultant deterioration of copy quality. In order to conserve air, these devices are normally employed in a pulse mode which requires timing in relationship to the lead edge of the sheet to be stripped. This timing must be accurate. If the blast of air occurs too soon, the energy has been exhausted before the lead edge of the sheet of material arrives. If the blast occurs too late, the air will actually push the material down on the photoreceptor rather than remove it therefrom. Normally, these air nozzels are not capable of discharging the complete air blast below the lead edge of the sheet; some of the air will always react against the top of the sheet and tend to push the sheet down against the photoreceptor surface.
Mechanical stripping devices such as those disclosed in U.S. Pat. Nos. 3,578,859 and 3,450,402 have been used for quite some time in the copying art with varying degrees of success. However, mechanical stripping devices must be accurately aligned and through use may be subject to misalignment problems whereby the stripping mechanism fails to act upon the sheet at the proper place. As a result, the sheet either remains on the support surface or is distorted during the removal operation, thus causing the machine to malfunction. Further, where a mechanical pickoff finger is introduced between the photoreceptor and the sheet material carried thereon, misalignment of the finger can also cause the finger to contact and abrade the relatively delicate photosensitive plate surface thereby necessitating frequent replacement of the photoreceptor. In designing stripper fingers and the mounts therefore, one of the primary considerations must be the provision of a structure which will minimize bounce during the moment of stripping and be capable of lifting the copy off the photoreceptor without smudging the image and without damaging the photoreceptor.
To minimize wear on the photoreceptor surface it is desirable to move the stripper finger out of operating position after stripping has been accomplished. Many devices heretofore utilized having various pivots, crank pins etc. have a tendency to become contaminated with toner resulting in sluggish movement of the finger toward the photoreceptor surface. This may cause the stripper finger to miss the lead edge of the sheet material to be stripped. Further, in those stripper finger constructions wherein the stripper finger is solidly mounted on crank pins and arms, the impact force of the copy against the finger is transmitted directly against the photoreceptor and the underside of the stripper finger, causing undesirable wear and premature failure of the photoreceptor and stripping finger.
It is therefore an object of the present invention to provide a movable stripper finger, the operation of which is not effected by contamination with materials such as toner and paper fibers, which will absorb impact loading during stripping to prevent the impact from being translated into a high loading of the tip against the support surface and which is not subjected to misalignment or bounce during operation of the machine.